Archive | Computer Science

VHS is dead. If you don’t have a functioning VHS player any more, your only option is to buy second-hand devices. But if you still have old, valuable VHS videos (e.g. family videos) you should digitize them today, as long as there are still working VHS players around. Our goal is to feed the audio/video […]

For a project of mine, I needed a ‘headless’ script that renders dynamically generated HTML (via JavaScript) to a PDF file. In looking for existing headless browsers, I found PhantomJS, CasperJS and similar projects. PhantomJS looked most promising, but it had bugs related to the CSS @media type ‘print’ which made the project useless for […]

This is a simple but fully scriptable headless QtWebKit browser using PyQt5 in Python3, specialized in executing external JavaScript and generating PDF files. A lean replacement for other bulky headless browser frameworks. (Source code at end of this post as well as in this github gist) Usage If you have a display attached:

Sometimes programmers hesitate to make their software open source because they think that revelation of the source code would allow attackers to ‘hack it’. Certainly there are specific cases where this is true, but not as a general rule. In my opinion, if inspection of the source code allows an attacker to ‘hack it’, then […]

There are certain cases where you want to operate a not completely trusted networked machine, and write scripts to automate some task which involves an unattended SSH login to a server. With “not completely trusted machine” I mean a computer which is reasonably secured against unauthorized logins, but is physically unattended (which means that unknown […]

It could be said that SSH (Secure Shell) is an administrator’s most important and most frequently used tool. SSH uses public-key cryptography to establish a secure communication channel. The public/private keypair is either generated automatically, where the (typed or copy-pasted) plaintext password is transmitted over the encrypted channel to authenticate the user, or generated manually […]

In a previous blog post I argued that a good backup solution includes backups at different geographical locations to compensate for local desasters. If you don’t fully trust the location, the only solution is to keep an encrypted backup. In this tutorial we’re going to set up an encrypted, mountable backup image which allows us […]

Why should you regularly make backups? Because if you don’t, then this mistake will bite you, sooner or later. Why? Because of Murphy’s Law: Anything that can go wrong, will go wrong. And a variation of it, Finagle’s law, even says: Anything that can go wrong, will—at the worst possible moment. So, let’s prepare right now and […]

Dropbear is a replacement for standard OpenSSH for environments with low memory and processor resources. With OpenSSH, you can use the well-known
ssh-keyen command to create a private/public keypair for the client. In Dropbear, it is a bit different. Here are the commands on the client: